The present invention relates to a vapor reflow soldering apparatus and more particularly to a vapor fellow soldering apparatus which is suitable for high density packaging for soldering so-called flat package ICs having electrode terminals which are led flatly on each printed circuit board in four directions and resistor and capacitor surface mount devices.
Recently, electronic parts are packaged in high density increasingly on printed circuit boards. However, the soldering operation for bonding electronic parts such as semiconductors and devices to printed circuit boards is the last process of the line, so that the soldering art is assumed as a most important art of the line. Since it is necessary to increase the uniformity of temperature distribution in a furnace where the soldering operation is performed and to avoid overheat which is harmful for electronic parts, a vapor fellow soldering apparatus which uses vapor with high specific gravity to air as a thermal medium and heats an article to be processed using the latent heat of condensation is used recently.
This apparatus is, as indicated, for example, in Japanese Patent Laid-Open No. 63-90361, a soldering apparatus having a vapor generating tank for soldering a printed circuit board by passing it through saturated vapor of a thermal medium with high specific gravity to air as mentioned above.
A conventional typical vapor reflow soldering apparatus using a conveyor will be explained with reference to FIGS. 4 and 5.
FIG. 4 is a vertical sectional view of a conventional vapor reflow soldering apparatus and FIG. 5 is a sectional view taken on the A--A line shown in FIG. 4.
The apparatus shown in FIG. 4 has a reflow chamber 1 including a vapor generating tank 4, an inlet-side delivery path 5, an outlet-side delivery path 6, a heater 7, an inlet-side cooling coil 8, an outlet-side cooling coil 9, an inlet-side exhaust port 10, and an outlet-side exhaust port 11, a preheating chamber 2 including a preheater 14, a cooling chamber 3 including a cooling fan 18, a driving unit including a conveyor 15, a drive sprocket 19, an inlet-side sprocket 20, and an outlet-side sprocket 21, a thermal medium recovering system including a recovery tank 23, a water/acid remover 26, a controller 27 and a pump 27a, and a filtering system (not shown in the drawing) for removing flux which gets mixed in a thermal medium 12 in the vapor generating tank 4.
The operation of a conventional vapor reflow soldering apparatus which has the above structure will be explained hereunder.
Saturated vapor 13 of the thermal medium 12 which is boiled and vaporized by the heater 7 immersed in the thermal medium 12 collected at the bottom of the vapor generating tank 4 moves up and is discharged from a side vapor outlet 32 leading to a side wall path 31 and from a lower vapor outlet 33 so as to heat an article 16 to be processed on the conveyor 15 as shown in FIG. 5. A part of the saturated vapor is condensed and liquefied, and drops, and is collected at the bottom of the vapor generating tank 4. The saturated vapor 13 which flows into the inlet-side delivery path 5 and the outlet side delivery path 6 is cooled and liquefied by the inlet side cooling coil 8 and the outlet-side cooling coil 9 and returned to the bottom of the vapor generating tank 4 via a return pipe 17.
A small amount of remaining vapor flows into the recovery tank 23 from the inlet-side exhaust port 10 and outlet-side exhaust port 11 via a pipe 22 and vapor which is adhered to and separated later from the article 16 to be processed flows into the recovery tank 23 from the outlet-side exhaust port 11 via the pipe 22. The above vapor is cooled by a cooling coil 24 in the recovery tank 23 and the thermal medium in mist phase state is acquired by a demister 25 for removing mist and dropped and collected at the bottom.
The collected thermal medium flows into the water/acid remover 26 via a pipe 22a. The thermal medium is separated from water/acid by the water/acid remover 26 and the floated water/acid overflow. When the thermal medium collected at the bottom reaches a fixed amount, a controller 27 operates on the basis of a detection signal of a detection means such as a float switch and the thermal medium is returned to the vapor generating tank 4 via a pump 27a and a pipe 22b.
On the other hand, the article 16 to be processed which is heated by the preheater 14 and delivered into the reflow chamber 1 from the preheating chamber 2 by the conveyor 15 comes in contact with saturated vapor 13 and is heated. In the vapor generating tank 4, solder is heated and melted by the latent heat of condensation of the saturated vapor 13 and the article 16 is soldered. The article 16 to be processed is sent into the outlet-side delivery path 6, cooled gradually, sent into the cooling chamber 3, cooled furthermore by the cooling fan 18, and then transferred from the equipment.
The saturated vapor 13 in the vapor generating tank 4 is kept constant in temperature by controlling the power supplied to the heater 7 by a temperature sensor 28 which is movable inside the vapor generating tank 4 and a temperature controller 29 via a power regulator 30.
Exhaust gas which passes through the demister 25 of the recovery tank 23 may contain a small amount of thermal medium mist. Therefore, the thermal medium is acquired additionally by a processor so as to acquire and collect thermal medium in fine mist phase state and exhaust gas is discharged into the atmosphere after the thermal medium is fully removed.
The following problems are imposed in the aforementioned vapor reflow soldering apparatus.
According to the structure that the saturated vapor 13 which is a heat source in the outlet-side delivery path 6 is reduced in volume by condensation by the outlet-side cooling coil 9 and cooled, the cooling speed for the article 16 to be processed is slow compared with a hot air reflow soldering apparatus for blowing off hot air and the bonding strength of the soldered part is low.
The vapor reflow soldering apparatus indicated in U.S. Pat. Nos. 5,146,694 and 5,156,325 (the inventors of both patents are the same as the inventors of the present invention, so that these patents are not prior arts for the present application). also has the above problems.